Roll-changing means for four-high rolling mill

ABSTRACT

Roll changing means for a four-high rolling mill for automatically and rapidly changing top and bottom working rolls and top and bottom backup rolls without necessitating the use of a crane by combining a working roll changing truck and a backup roll changing truck in a double-sled shifted sidewise manner.

O United States Patent [151 3,638,468

Fukui et al. Feb. I, 1972 [54] ROLL-CHANGING MEANS FOR FOUR- [56]References Cited HIGH ROLLING MILL UNITED STATES PATENTS [72] Inventors:Eukui; Shiro lmai, both of 3,221,530 12/ 1965 Swallow et al ..72/239Japan 3,312,096 4/1967 Stubbs et a1. ..72/23s Assignee: Hitachi LtdTokyo Japan Beard 3,518,862 7/1970 Dehaine et al ..72/238 [22] Filed:Sept. 30, 1969 21 A L N 862,331 Primary Examiner-Charles W. Lanham 1 pp0 Assistant Examiner-B. J. Ollila Attorney-Craig, Antonelli and Hill[30] Foreign Application Priority Data Oct. 2, 1968 Japan ..43/71 121[57] ABSTRACT Roll changing means for a four-high rolling mill forautomati- {521 US. Cl ..72/238, 72/239 ally an rapidly changing t p nbottom w rking r ll n [5 l Int. Cl ..B2lb 31/10 p and bottom backuprolls Without necessitating the use Of a [58] 72/237, 233, 239 crane bycombining a working roll changing truck and a Field of Search backupr011 changing truck in a double-sled shifted sidewise manner.

17 Claims, 4 Drawing Figures I. n II I; 42

VI 3} I] I E" 3 35 39 7 26 PATENTED FEB 7 i972 SHEU 2 0F 4 ROLL-CHANGINGMEANS FOR FOUR-HIGH ROLLING MILL y matically change a top and a bottomworking roll and a top and a bottom backup roll of a four-high rollingmill, the changing operation being performed rapidly and efficientlywithout necessitating the use of a crane.

Hithertofore, since the operation for changing working rolls of arolling mill has been performed by using a roll-changing jig, such as aporter bar, a C-hook and the like to remove and replace one or moreworking rolls, it has been always necessary to use a crane, andincreased labor hours and highly skilled workmen were required.

In order to solve the above mentioned problems, there have been proposeda turntable-type roll changing means as disclosed in the US. Pat. No.3,208,260 and a double-sled-type roll-changing means as disclosed in theUS. Pat. No. 3,3l2,096. However, the turntable type is complicated inits mechanism and requires an increased space, so that it cannot bepractically employed in a continuous rolling mill in which the distancebetween each roll stand unit is small. Further, in a four-high rollingmill, even when the turntable-type is used for changing working rolls,C-hook and the like is used for changing backup rolls.

Further, in applying the double-sled type in a four-high rolling mill,when it is desired to change backup rolls, working roll-changing trucksshould necessarily be transferred transversely in order to providespaces for performing the operation for changing the backup rolls.Particularly, in a continuous rolling mill, since the spaces fortransversely transferring the trucks are limited, it was only possibleto employ, as far as the backup rolls are concerned, an essentiallysingle sled type in which the rolls are withdrawn from rolling millstand and thereafter hoisted by an overhead travelling crane to bereplaced by new backup rolls.

Thus, in a four-high rolling mill, in order to remove and replace topand bottom working rolls and top and bottom backup rolls by either ofthe conventional changing means, a crane operation using a C-hook andthe like is required and it is difficult to decrease the time requiredfor the changing "operation and thus to increase the operationalefficiency of the rolling mill.

f The primary object of the present invention is to provide rollchanging means for a four-high rolling mill in which top and bottomworking rolls and top and bottom backup rolls can be automatically,rapidly and efficiently removed and replaced in a double-sled mannerwithout necessitating the use of any crane operation during changingoperation.

Another object of the present invention is to provide roll changingmeans in which a working roll-changing truck and a backup roll-changingtruck are so combined that the space occupied by the means, particularlythe distance through which the rolls are transversely transferred, issubstantially decreased and that the means can be employed in acontinuous rolling mill.

According to one aspect of the present invention, there is providedroll-changing means for a four-high rolling mill comprising meansprovided in a rolling mill stand in parallel relation with a roll axisfor supporting the roll for axial movement when it is removed andreplaced, lifting means for placing said roll on said support means whenthe roll is being removed and replaced, transfer means for axiallytransferring the roll from and into the rolling mill stand, a workingroll-changing truck provided outside the rolling mill stand for carryingused and new working rolls, a backup roll-changing truck for carryingsaid working roll-changing truck and used and new backup rolls,transverse transfer means for transferring said backup roll-changingtruck in the direction perpendicular to the m ll axis so as to changethe relative position of the used and backup rolls, means for enablingthe transverse transfer means to he used for transversely transferringthe working roilchanging truck, and retracting means for retracting saidworking roll-changing truck when the backup roll is being changed.

The present invention will now bedesc'ribed with respect to anembodiment thereof taking reference to the accompanying drawings, inwhich:

FIG. I is a front view of a four-high rolling mill embodying theroll-changing means'of the present invention;

FIG. 2 is a side view thereof;

FIG. 3 is a plan view of FIG. 2;

FIG. 4 is a sectional view taken along the line lV-IV of FIG. 3; and, 3FIG. 5 is a sectional view taken along the line V-V of FIG.

Referring to the drawings, the numeral I shows a rolling mill stand, and2 and 3 show a top and a bottom backup rolls respectively which areassembled in a window 1 formed in the rolling mill stand I. The backuprolls 2 and 3 can be moved axially through said window I when it isdesired to replace them by another pair of rolls. The numerals 2' and3"show another pair of backup rolls which are to be assembled in theplace of the backup rolls 2 and 3, and 4 and 5 show top and bottomworking rolls which can be moved axially through the window I. Thenumerals 4' and 5' are another pair of top and bottom working rollswhich are placed on a working roll-changing truck which will bedescribed later. The numerals 6 and 7 show bearing chocks provided atthe journal of the top and bottom backup rolls 2 and 3, and 8 and 9 showbearing chocks at the ends of the top and bottom working rolls 4 and 5.The numeral 10 is a carrier which is connected with a balance cylinder(not shown) of said top backup rolls 2 and adapted to the top backuproll 2 so that a space is provided for facilitating the roll changingoperation, 11 a screwed member of screwdown mechanism, and 12 aprotecting cover. The numeral 13 shows balance cylinders providedbetween the Bizaring chocks 8 and 9 of the top and bottom working rollsrespectively, and 14 shows roll changing rails for the top and bottomworking rolls 4 and 5. The rails 14 are disposed at the opposite sidesof the window I of the rolling mill stand 1 in parallel relation withroll axis and held during rolling operation by the bearing chock 7 ofthe bottom backup roll 3. The rails 14 are so arranged that they arepushed upwardly to a predetermined position by hydraulic cylinders 16when it is desired to replace the top and bottom working rolls 4 and 5.The hydraulic cylinders 16 are provided at the opposite sides of therolling mill stand I. The numeral 15 shows positioning stoppers for theroll-changing rails I4 which are lifted by the hydraulic cylinder I6,and 17 shows wheels mounted on the bearing chock 9 of the bottom workingroll 5. The wheels I7 rotate along the roll changing rails 14 when thetop and bottom working rolls 4 and 5 are being replaced. The numeral I8shows a traction car which is integrally connected with the bearingchocks 8 and 9 and adapted to carry the top and bottom working rolls 4and 5 into and from the rolling mill stand I. The traction car 18 isdisposed along a line parallel to the roll axis. The numeral 19 is aworking roll-changing truck for carrying new working rolls which are tobe moved into the rolling mill stand I, used working rolls which are tobe moved out of the rolling mill stand I, and a stool 45 which is to beinserted between the bearing chocks 6 and 7 of the top and bottom backuprolls 2 and 3 respectively. The truck I9 is so arranged adjacent to theoperating side of the rolling mill stand I that its upper surface formsan aligned continuous plane with the upper surface of the rails 14 whenthe rolls are being removed and replaced. The numeral 20 shows avertically movable floor plate carrying traction car 18, and 22 showsrails provided on the floor plate 20. The car 18 is movable along therails 22. The car I8 is driven along the rails 21 and 22 provided on theworking roll changing truck 19 and the floor plate 20 respectively bythe rotation of an electric motor 1 23 which is transmitted through wormgear means (not shown), a pinion shaft 24 and racks 25 and 25' providedon the working roll-changing truck 19 and the floor plate 20respectively. The numeral 26 shows a backup roll changing truck forcarrying the working roll changing truck 19 and the unused backup rolls2' and 3'. The truck 26 is transversely movable sidewise to the rollaxis. The truck 26 is provided with sliding surfaces 27 and 28 forcarrying the backup roll for sliding movement in the direction of rollaxis, and with a plurality of rails 29 for carrying the working rollchanging truck 19 for movement in the direction of roll axis. The backuprollchanging truck 26 is further slidably mounted on supportingpedestals 31 and 31' and can be transversely moved in the directionperpendicular to the roll axis by hydraulic cylinder 30. The numerals 32and 32' show stoppers for the trucks 26 provided at the opposite ends ofthe supporting pedestals 31 and 31 and 33 and 33' show intermediatestoppers which can be adjusted in position by a hydraulic cylinder 34and is adapted to limit the transverse travel of the backup rollchanging truck 26. The numeral 35 shows a changing sled for carry ingthe bearing chock 7 of the bottom backup roll 3, 36 a frame forconnecting the operating side sled 35 and a sled on the drive side (notshown), and 37 an intermediate supporting pedestal for guiding the topand bottom backup rolls 2 and 3 from the rolling mill stand 1 to thebackup roll changing truck 26 when the rolls are being changed. Thepedestal 37 is so arranged that its upper surface aligns with the lowersurface of said sled 35 and the upper surface of the truck 26. Thenumeral 38 shows a hydraulic cylinder for moving the top and bottombackup rolls 2 and 4 from and into the rolling mill stand 1, 39 a hookfor connecting the hydraulic cylinder 38 and the sled 35, 40 an armextending from the lower side of the working roll changing truck 19, and41 a hook rotatably mounted on said arm 40 for connecting the workingrollchanging truck 19 with the sled 35. By this hook 41, the workingrollchanging truck 19 can be moved rearwardly simultaneously when thetop and bottom backup rolls 2 and 3 are moved outwardly from the rollingmill stand 1. The numeral 42 shows a hydraulic cylinder for effectingthe vertical movement of the floor plate 20, and 43 shows shunt railsprovided on the base below the floor plate 20 at a lever the same as therails 29 for carrying the truck 19. The shunt rails are provided forretracting the working roll-changing truck 19 from the backuproll-changing truck 26 when the backup rolls 2 and 3 are being changed.The numeral 44 shows shunt rails provided at a level same as the rails22 for carrying the traction car 18. The shunt rails 44 are provided forretracting the car 18 and the working rolls 4 and rearwardly. Thenumeral 45 shows a stool adapted to be inserted between the backup rolls2 and 3 after the working rolls 4 and 5 are retracted from the rollingmill stand I, 46 a stool inserted between the top and bottom backuprolls 2' and 3', and 47 a hook for connecting the traction car 18 andthe bottom working roll 5.

When it is desired to remove and replace the working rolls 4 and 5, thetop backup roll 2 is upwardly moved by the balance cylinder (not shown)through the carrier beam to provide a space required to change therolls. Then, the rails 14 are moved upwardly by the hydraulic cylinders16 until they engage with the stoppers l5, and the top and bottomworking rolls 4 and 5 are placed on the rails 14. In this position, theupper surface of the rails 14 and the upper surface of the rails 21 ofthe truck 19 align with each other. Thereafter, the top and bottomworking rolls 4 and 5 with the bearing chocks 8 and 9 are slidably movedby the traction car 18 along the rails 14 onto the rails 21 from therolling mill stand 1. Prior to this step, a new set of top and bottomworking rolls are placed on the rail 21' of the working roll changingtruck 19. (The drawings show a position in which the backup rolls arebeing changed, so that the stool 45 is disposed on the rail 21'.Further, a new pair of backup rolls 2' and 3' are disposed on thesliding surface 27 of the truck 26. However, when only the working rollsare to be changed, they may be omitted and the sliding surface 27 may beleft free of rolls). Thus, when the top and bottom working rolls 4 and 5are completely transferred on the truck 19, the hydraulic cylinder 30 isactuated to move the working roll changing truck 19 together with thetruck 26 in the direction perpendicular to the roll axis until the axesof the new working rolls align with the center of the rolling mill.

Inthis case, in order to determine the transversely transferred positionof the trucks, the intermediate stoppers 33 are used.

Thus, the truck 26 can only be moved to the position in which 5 itengages with the stoppers 33. Thereafter, the traction car 18 isoperated and the new working rolls are moved into the rolling millstand 1. Then, the changing rails I4 are lowered by the hydrauliccylinder 16 and the backup rolls 2 are returned to its initial positionby the balance cylinder (not shown) which acts through the carrier beam10. Finally, the screw II is adjusted and thus the rolling mill becomesready for operation. The removed working rolls 4' and 5' are transferredby the traction car 18 to a suitable position and from there they arecarried by a crane.

The operation in which the backup rolls are removed and replaced willnow be described. The stool 45 is placed on the rails 21' of the workingroll-changing truck 19 and a pair of new backup rolls 2' and 3 withmetal chocks are mounted on the sliding surface 27 of the backuproll-changing truck 26. The stool 46 is interposed between the saidbearing chocks. When the upper and lower working rolls 4 and 5 aretransferred to the working roll changing truck 19 as shown by 4' and 5'in the drawings through the steps of the abovedescribed workingroll-changing operation, the hook 47 is disconnected with the tractioncar 18 placed on the rails 22 and thereafter the hydraulic cylinder 30is actuated to move the backup roll-changing truck 26 and the workingroll-changing truck 19 in the direction perpendicular to the rollaxisuntil the center of the stool 45 aligns with the center'of the rollingmill or until the trucks are stopped by the intermediate stopper 33. Inthis position, the traction car 18 is again operated so as to move thespacer 45 into the rolling mill stand 1 through the intervention of thehook 47. Thereafter, the car lowered by the hydraulic cylinder 16 untilthe stool 45 is placed on the bearing chocks 7 of the bottom backup roll3. The top backup roll 2 is further lowered through the carrier beam 10until its metal chocks 6 rides on said stool 45.

The removed working rolls 4' and 5' are placed on the working rollchanging truck 19 when the stool 45 is being moved into the rolling millstand 1, and when the backup rollchanging truck 26 is moved with theworking roll-changing truck 19 to the position shown in FIG. 3 in whichthe truck 26 is stopped by the stoppers 32, the rolls 4' and 5' aretransferred along the rails 21 of the working roll changing truck I9 andthe rails 22 of the floor plate 20 onto the shunt rails 44. Thereafter,the floor plate 20 is lifted by the hydraulic cylinder 42 to provide aspace for receiving the truck 19. Then, the top and bottom backup rolls2 and 3 with bearing chocks are removed as a unit from the rolling millstand 1 by the hydraulic cylinder 38 which acts through the hook 39 andthe sled 35, and are transferred through the intermediate supportingpedestal 37 to the sliding surface 28 of the backup roll-changing truck26. In this instance, since the work roll changing truck 19 is connectedwith the sled 35 by the hook 41, the truck 19 is moved on the shuntrails 43 provided below the floor plate 20 simultaneously as the backuprolls 2 and 3 are removed from the rolling mill stand. Therefore, theworking roll-changing truck 19 does not interfere with the backup rollswhen the rolls are moved onto the truck 26. Thereafter, the hooks 39 and41 are opened to disconnect the sled 35.

Then, the intermediate stopper 33 is moved away from the operativeposition by the hydraulic cylinder 34, and the hydraulic cylinder 30 isactuated to move the backup rollchanging truck 26 until it engages withthe stoppers 32'. Thus, the center of the new backup rolls 2 and 3'comes into alignment with the center of the rolling mill. Thereafter,the hook 39 is connected with the changing sled 35' of the new backuprolls 2' and 3', and the hydraulic cylinder 38 is actuated to move therolls 2 and 3' into the rolling mill stand 1. After the backup rolls aremoved into the rolling mill stand, said top and bottom backup rolls 2and 3 are carried out by a crane, and the backup roll-chaning truck 26is transversely moved until it 18 is again returned on the rails 22.Then, the rails 14 are engages with the intermediate stopper 32.Thereafter, the hook 39 and the arm 40 are connected with each other,and the hydraulic cylinder 38 is actuated to move the working changingtruck 19 onto the backup roll-changing truck 26. The floor plate 20 isthen lowered to the original position by the hydraulic cylinder 42. Fromthis position, the removed working rolls 4' and 5' are transferred bythe traction car 18 from the shunt rail 43 through the rail 22 to therail 21 of the working roll-changing truck 19. As the next step, theupper backup roll in the rolling mill stand 1 is lifted by the balancecylinder (not shown) through the carrier beam 10, and the rail 14 islifted to a predetermined position by the hydraulic cylinder 16.Thereafter, as in the working roll-changing operation, the stool 46which has been moved into the rolling mill stand is replaced by the topand bottom working rolls 4 and 5' by using the traction car 18. Then,the balance cylinder for the backup roll (not shown) and the balancecylinder 13 for the working roll are actuated, and the screw 11 of thescrewdown mechanism is adjusted as required. Thus, the rolling millbecomes ready for operation.

The present invention has been described and illustrated with referenceto a preferred embodiment, however, it should of course be understoodthat the embodiment is merely an example and various changes andmodifications may be made without departing from the spirit and scope ofthe present invention.

We claim:

1. Roll-changing means for a four-high rolling mill comprising meansprovided in a rolling mill stand in parallel relation with a roll axisfor supporting the roll for axial movement when it is removed andreplaced, lifting means for placing said roll on said support means whenthe roll is being removed and replaced, transfer means for axiallytransferring the roll from and'into the rolling mill stand, a workingroll-changing truck provided outside the rolling mill stand for carryingused and new working rolls, a backup roll-changing truck for carryingsaid working roll-changing truck and used and new backup rolls,transverse transfer means for transferring said backup roll-changingtruck in the direction perpendicular to the roll axis so as to changethe relative position of the used and new backup rolls, means forenabling the transverse transfer means to be used for transverselytransferring the working rollchanging truck, and retracting means forretracting said working roll-changing truck in a direction substantiallyparallel to said roll axis when the backup roll is being changed.

2. Roll-changing means for a four-high rolling mill in accordance withclaim I, in which said lifting means comprises hydraulic cylinders andlinkages provided at the opposite sides of the rolling mill stand forvertically moving said support means.

3. Roll-changing means for a four-high rolling mill in accordance withclaim 2, in which the transfer means for axially moving the top andbottom work rolls includes a traction car which is arranged so as tomove along rails which are provided outside the rolling mill stand andin alignment with roll-changing rails in the rolling mill stand.

4. Roll-changing means for a four-high rolling mill in accordance withclaim 3, in which said traction car includes an electric motor and amechanism for transferring the rotation of the motor, a pinion shaft inthe mechanism being arranged to engage with racks provided on theworking roll-changing truck and a floor plate.

5. Roll-changing means for a four-high rolling mill in accordance withclaim 3, in which the rails along which the traction car moves comprisesrails provided on the working rollchanging truck outside the rollingmill stand, rails provided on a floor plate which is behind the workingroll-changing truck, and shunt rails provided further rearwardly of saidfloor plate.

6. Roll-changing means for a four-high rolling mill according to claim5, in which the transfer means for axially moving the top and bottombackup rolls comprises a hydraulic cylinder, a sled for carrying bearingchocks of the bottom backup roll and a hook for connecting the hydrauliccylinder and the sled.

7. Roll-changing means for a four-high rolling mill accord ing to claim6, in which said working roll-changing truck is mounted for movement inthe direction of roll axis on the backup roll-changing truck and has onits upper surface two sets of rails for supporting the used and newworking rolls and a stool inserted between the top and bottom backuprolls.

8. Roll-changing means for a four-high rolling mill according to claim7, in which the backup roll-changing truck is slidably mounted onpedestals on the base so as to be transversely moved by the hydrauliccylinder in the direction perpen dicular to the roll axis.

9. Roll-changing means for a four-high rolling mill in accordance withclaim 8, in which said backup roll-changing truck is provided with asliding surface for carrying the backup rolls for sliding movement inthe direction of roll axis and a plurality of rails for carrying theworking roll-changing truck for movement in the direction of roll axis.

10. Roll-changing means for a four-high rolling mill in accordance withclaim 8, in which the pedestal is provided with a pair of stoppersprovided at the opposite sides thereof for limiting the transversetransfer distance of the backup rollchanging truck and a pair ofintermediate stoppers which can be selectively moved into and out of theoperative position.

11. Roll-changing means for a four-high rolling mill in accordance withclaim 1, in which an intermediate pedestal is provided between therolling mill stand and the backup rollchanging truck for guiding thebackup rolls, the intermediate pedestal being so arranged that its uppersurface aligns with the lower surface of the sled for the backup rolland the sliding surface on the backup roll-changing truck.

12. Roll-changing means for a four-high rolling mill in accordance withclaim 11, in which the sled for the backup roll can be connected withthe working roll-changing truck by means of a rotatable hook whereby theworking roll-changing truck is rearwardly moved simultaneously when thebackup rolls are moved from the rolling mill stand to the backuprollchanging truck.

13. Roll-changing means for a four-high rolling mill in accordance withclaim 5, in which the floor plate located rearwardly of the workingroll-changing truck is vertically movable, the floor plate being movedupwardly to provide a space for receiving the working roll-changingtruck.

14. Roll-changing means according to claim 9, in which said transfermeans comprises means for axially moving the top and bottom workingrolls and means for axially moving the top and the bottom backup rollsand wherein said traction car includes an electric motor and a mechanismfor transferring the rotation of the motor, a pinion shaft in themechanism being arranged to engage with racks provided on the workingrollchanging truck and a floor plate.

15. Roll-changing means according to claim 14, in which the pedestal isprovided with a pair of stoppers provided at the opposite sides thereofwhile limiting the transverse transfer distance of the backuproll-changing truck and a pair of intermediate stoppers which can beselectively moved into and out of the operative position, and in whichthe floor plate located rearwardly of the working roll-changing trunk isvertically movable the floor plate being moved upwardly to provide aspace for receiving the working roll-changing truck.

16. Roll-changing means according to claim 15, in which an intermediatepedestal is provided between the roll mill stand and the backuproll-changing truck for guiding the backup rolls, the intermediatepedestal being so arranged that its upper surface aligns with the lowersurface of the sled for the backup roll and the sliding surface on thebackup roll-changing truck.

17. Roll-changing means according to claim 16, in which the sled for thebackup roll is connectable with the working roll-changing truck by meansof a rotatable hook, whereby the working roll-changing truck isrearwardly moved simultaneously when the backup rolls are moved from therolling mill stand to the backup roll-changing truck.

1. Roll-changing means for a four-high rolling mill comprising meansprovided in a rolling mill stand in parallel relation with a roll axisfor supporting the roll for axial moveMent when it is removed andreplaced, lifting means for placing said roll on said support means whenthe roll is being removed and replaced, transfer means for axiallytransferring the roll from and into the rolling mill stand, a workingroll-changing truck provided outside the rolling mill stand for carryingused and new working rolls, a backup roll-changing truck for carryingsaid working roll-changing truck and used and new backup rolls,transverse transfer means for transferring said backup roll-changingtruck in the direction perpendicular to the roll axis so as to changethe relative position of the used and new backup rolls, means forenabling the transverse transfer means to be used for transverselytransferring the working roll-changing truck, and retracting means forretracting said working roll-changing truck in a direction substantiallyparallel to said roll axis when the backup roll is being changed. 2.Roll-changing means for a four-high rolling mill in accordance withclaim 1, in which said lifting means comprises hydraulic cylinders andlinkages provided at the opposite sides of the rolling mill stand forvertically moving said support means.
 3. Roll-changing means for afour-high rolling mill in accordance with claim 2, in which the transfermeans for axially moving the top and bottom work rolls includes atraction car which is arranged so as to move along rails which areprovided outside the rolling mill stand and in alignment withroll-changing rails in the rolling mill stand.
 4. Roll-changing meansfor a four-high rolling mill in accordance with claim 3, in which saidtraction car includes an electric motor and a mechanism for transferringthe rotation of the motor, a pinion shaft in the mechanism beingarranged to engage with racks provided on the working roll-changingtruck and a floor plate.
 5. Roll-changing means for a four-high rollingmill in accordance with claim 3, in which the rails along which thetraction car moves comprises rails provided on the working roll-changingtruck outside the rolling mill stand, rails provided on a floor platewhich is behind the working roll-changing truck, and shunt railsprovided further rearwardly of said floor plate.
 6. Roll-changing meansfor a four-high rolling mill according to claim 5, in which the transfermeans for axially moving the top and bottom backup rolls comprises ahydraulic cylinder, a sled for carrying bearing chocks of the bottombackup roll and a hook for connecting the hydraulic cylinder and thesled.
 7. Roll-changing means for a four-high rolling mill according toclaim 6, in which said working roll-changing truck is mounted formovement in the direction of roll axis on the backup roll-changing truckand has on its upper surface two sets of rails for supporting the usedand new working rolls and a stool inserted between the top and bottombackup rolls.
 8. Roll-changing means for a four-high rolling millaccording to claim 7, in which the backup roll-changing truck isslidably mounted on pedestals on the base so as to be transversely movedby the hydraulic cylinder in the direction perpendicular to the rollaxis.
 9. Roll-changing means for a four-high rolling mill in accordancewith claim 8, in which said backup roll-changing truck is provided witha sliding surface for carrying the backup rolls for sliding movement inthe direction of roll axis and a plurality of rails for carrying theworking roll-changing truck for movement in the direction of roll axis.10. Roll-changing means for a four-high rolling mill in accordance withclaim 8, in which the pedestal is provided with a pair of stoppersprovided at the opposite sides thereof for limiting the transversetransfer distance of the backup roll-changing truck and a pair ofintermediate stoppers which can be selectively moved into and out of theoperative position.
 11. Roll-changing means for a four-high rolling millin accordance with claim 1, in which an intermediate pedestal isprovided between the rolling mill Stand and the backup roll-changingtruck for guiding the backup rolls, the intermediate pedestal being soarranged that its upper surface aligns with the lower surface of thesled for the backup roll and the sliding surface on the backuproll-changing truck.
 12. Roll-changing means for a four-high rollingmill in accordance with claim 11, in which the sled for the backup rollcan be connected with the working roll-changing truck by means of arotatable hook whereby the working roll-changing truck is rearwardlymoved simultaneously when the backup rolls are moved from the rollingmill stand to the backup roll-changing truck.
 13. Roll-changing meansfor a four-high rolling mill in accordance with claim 5, in which thefloor plate located rearwardly of the working roll-changing truck isvertically movable, the floor plate being moved upwardly to provide aspace for receiving the working roll-changing truck.
 14. Roll-changingmeans according to claim 9, in which said transfer means comprises meansfor axially moving the top and bottom working rolls and means foraxially moving the top and the bottom backup rolls and wherein saidtraction car includes an electric motor and a mechanism for transferringthe rotation of the motor, a pinion shaft in the mechanism beingarranged to engage with racks provided on the working roll-changingtruck and a floor plate.
 15. Roll-changing means according to claim 14,in which the pedestal is provided with a pair of stoppers provided atthe opposite sides thereof while limiting the transverse transferdistance of the backup roll-changing truck and a pair of intermediatestoppers which can be selectively moved into and out of the operativeposition, and in which the floor plate located rearwardly of the workingroll-changing trunk is vertically movable the floor plate being movedupwardly to provide a space for receiving the working roll-changingtruck.
 16. Roll-changing means according to claim 15, in which anintermediate pedestal is provided between the roll mill stand and thebackup roll-changing truck for guiding the backup rolls, theintermediate pedestal being so arranged that its upper surface alignswith the lower surface of the sled for the backup roll and the slidingsurface on the backup roll-changing truck.
 17. Roll-changing meansaccording to claim 16, in which the sled for the backup roll isconnectable with the working roll-changing truck by means of a rotatablehook, whereby the working roll-changing truck is rearwardly movedsimultaneously when the backup rolls are moved from the rolling millstand to the backup roll-changing truck.